Hidden Subsets

Hidden Subsets are groups of digits that can appear only in a specific set of cells within one house. Once those cells are identified, every other candidate can be removed from them.

When to look for it

Look inside one row, column, or block and ask where each digit can still go. A Hidden Subset is easier to find by scanning digits than by scanning cells.

Implemented in Xodoku

Hidden Pair

Two digits can appear only in the same two cells of a house. Remove every other candidate from those two cells.

Hidden Triple

Three digits can appear only in three cells of a house. The cells do not need to contain all three digits individually.

Hidden Quadruple

Four digits can appear only in four cells of a house. Remove all other candidates from those cells.

Scope

Xodoku searches Hidden Pairs, Triples, and Quadruples. Larger hidden subsets are rare and usually show up as smaller or more direct deductions first.